In gear systems, such as automatic transmissions for motor vehicles, hydraulically actuated clutches are used for changing gears. For the sake of shifting that proceeds without bucking, and to make the course of shifting imperceptible to the driver, it is necessary that the hydraulic pressure at the clutches of the automatic transmission be in accordance with predetermined pressure ramps with extreme pressure precision. Electromagnetically actuated pressure regulating valves are used to adjust these pressure ramps. These pressure regulating valves are preferably embodied on the order of a seat. The requisite pressure level is achieved via a pressure balance that is integrated with the valve, and a force of the electromagnet that is variable as a function of current is brought into pressure equilibrium with the hydraulic force on the valve seat of the pressure regulating valve. To achieve the requisite pressure precision, it is necessary first that the valve seat be manufactured with high precision and second that the magnetic force, which is variable by means of the coil current of the pressure regulating valve, extend in accordance with a precise characteristic curve and that this characteristic curve maintain its characteristic even at different valve strokes.
From International Patent Disclosure WO 2004/036057 A2, a controllable magnet valve is known, in which the magnetic circuit is closed via a magnet yoke. In this version, a first sealing body in the interior of a valve housing is movable in the axial direction between two terminal positions relative to its first valve seat, an interaction between a magnetic force engendered by electric current and a spring force counteracting the magnetic force. The interior extends from an electromagnet to a terminal. To make purposeful, replicable variation of the outflow speed of cylinder controllers in hydraulic drives easily possible, and to avoid uncontrolled motions by these drives, the first sealing seat, toward the first sealing body, is provided with an axially extending cylindrical housing, in which a slide is adjusted axially as a function of the electric current. The cylindrical housing has radially oriented openings, such that these openings are closed when the first sealing body is located in one terminal position in its first sealing seat or in the immediate vicinity of the first sealing seat, and these openings are opened when the first sealing body is in the opposite terminal position. In the version known from WO 2004/036057 A2, radial magnetic transitions are established between a magnet yoke and a rotary part. As a result, on the one hand a greater number of parts is required, and furthermore, a plurality of assembly processes are necessary. Finally, there is an extra magnetic gap between a bush and the armature of the magnet valve.
From German Patent Disclosure DE 10 2005 014 100 A1, an electromagnetic valve is known, in particular for slip-controlled motor vehicle brake systems. The electromagnetic valve includes two valve closing bodies and a magnet armature that is embodied movably relative to the first valve closing body in order to reduce the amount of electromagnetic energy required. In this version, however, achieving a centering bush entails not inconsiderable additional expense. This furthermore requires magnetic transitions extending in the radial direction, thus entailing greater complexity and expense for assembly. For instance, the bush must be joined and connected in material-locking fashion. There is furthermore the need to create a press fit between the magnet yoke and the magnet core. In the version known from DE 10 2005 014 100 A1, as well, there is an extra magnetic gap between a bush and the armature of the electromagnetic valve.
From German Patent DE 196 32 552 C1, an adjusting device for the magnetic resistance of a magnetic circuit in a magnet valve is known. In this version, the armature is located displaceably in a nonmagnetic armature bush inserted into the carrier, and there is an annular gap between the armature bush and the carrier. A pole piece is embodied as a first bush of magnetic material, surrounding the armature bush. Into the annular gap between the armature bush and the carrier, plus to the first bush, a second bush of nonmagnetic material and a third bush of magnetic material are inserted; the third bush protrudes through the part of a short-circuit yoke that is located diametrically opposite the part adjacent to the third bush. Because of the magnetic transition occurring in the radial direction, two extra magnetic gaps are created between a yoke and the armature. Moreover, a radial pressure between the yoke and a bush requires great precision in producing the yoke bore. If this high-precision production is not assured, major variation in the magnet force occurs because of the ensuing air gap variations.